Documents FR-A-2 061 933 and U.S. Pat. No. 4,069,157 disclose filter devices in which the liquid to be filtered arrives via an inlet chamber at an inlet end of the block and flows along the channels to an outlet end and into an outlet chamber; the filtrate passes radially through the channel membranes and then through the block whose pore size is greater than that of the membrane, after which it is collected from the outside of the block; a residual liquid is collected from the outlet chamber and is recycled.
These devices suffer from leaks of the liquid to be filtered at the inlet and outlet ends of the block.
Between the channels at the inlet and outlet faces of the block, the liquid comes into contact with the large pore size block and a certain fraction of the liquid passes through the block to be collected with the filtrate, thereby reducing the purity of the filtrate. High purity can therefore be obtained only by performing a plurality of successive filtering operations. The larger the average diameter of the pores in the macroporous block, the higher the rate of leakage. Pore diameter in the block is generally about 4 .mu.m to 20 .mu.m.
The block could be mounted between parallel gaskets, however this gives rise to difficulties of assembly and it does not prevent residual leaks.
Document EP-A-0 154 295 describes a method of reducing leaks by filling the ends of the macroporous block with a microporous ceramic material, i.e. having pores with a diameter of about 1 .mu.m. However, although the method described does improve the situation, it nevertheless fails to obtain complete leakproofing at the end of the block. In any event, it is completely inadequate for ultrafiltration membranes or, a fortiori, for membranes having an organic separating layer, such as membranes for reverse osmosis or for pervaporation. This is clear in the case of ultrafiltration membranes since their pores have a diameter of not more than 0.1 .mu.m, i.e. much finer than the pores in the end filling material. If an attempt is made to avoid this problem by filling the end by means of a ceramic material having very small pores obtained by impregnating the end of the block by means of a suspension of very fine particles, it is difficult to control the penetration of such a fine slip into pores that are so large. There are also severe cracking problems due to shrinkage during sintering of the microporous material, and the smaller the particles to be sintered the greater the amount of shrinkage.
An object of the present invention is to provide a membrane separation device and in particular a filter device which enables a high-purity purified fluid to be obtained by leakproofing the ends of the macroporous block effectively and with good mechanical strength.